This invention relates to an ultrasonic vibration method and an ultrasonic vibration apparatus and, more particularly, to an ultrasonic vibration method and an ultrasonic vibration apparatus wherein a pair of ultrasonic horns coupled in an intersecting relationship to each other are used.
A bonding apparatus and a bonding method for an electronic part with bumps which utilizes ultrasonic vibrations are disclosed, for example, in Japanese Patent Laid-Open No. Hei 11-45912. Here, a pair of horns are disposed in an opposing relationship to each other on a common axis, and a piezoelectric element is attached to each of the horns. Further, an attracting tool is provided at the center of a narrow connecting portion intermediate between the opposing horns, and a semiconductor chip having bumps thereon is held by the attracting tool. Besides, the semiconductor chip here is resiliently held by and between a spring and a rib from a direction substantially perpendicular to the direction of the axis of the horns.
In the bonding apparatus and the bonding method described above, the semiconductor chip is subject to vibrations in the axial direction of the horns by the horns. In an initial stage, when the semiconductor chip is moved in the vibration direction with respect to a board, oxide films of the bumps and electrodes are broken. Then, as the bonding proceeds, the semiconductor chip slips with respect to the holding means formed from the spring and the rib as a result of an increase of the bonding force between the bumps and the electrodes, thereby to connect the bumps of the semiconductor chip and the electrodes of the board to each other.
Such an ultrasonic bonding apparatus as disclosed in Japanese Patent Laid-Open No. Hei 11-45912 has a problem in that, where it is used for bonding of a semiconductor chip, it sometimes fails to bond a semiconductor device of the type wherein a plurality of bumps are arranged in an arbitrary arrangement in such conditions that the bonding force of all of the bumps is higher than a desired value and no significant mechanical defect occurs. The ultrasonic bonding apparatus has a problem that, for example, if ultrasonic vibrations are applied to a semiconductor chip wherein bumps are arranged along a periphery of an electrode face of a semiconductor bare chip such that the vibration direction thereof is the same direction as that of one side of the rectangular bare chip, then if the bonding conditions are optimized so that the bonding strength of all bumps may be higher than a predetermined value, then those bumps disposed along the sides extending in the direction perpendicular to the application direction of the ultrasonic vibrations, particularly those bumps which are at corner portions of the rectangle of the bare chip, are likely to suffer from cratering.
Further, the ultrasonic bonding apparatus has a problem that, if the bonding conditions are set conversely so that such cratering as mentioned above may not occur with any of the bumps, then the bonding strength of those bumps that are disposed on the sides of the semiconductor chip which extend in parallel to the application direction of the ultrasonic vibrations does not reach a sufficient value. Such a phenomenon as just described appears conspicuously, particularly where a board having a low hardness such as, a glass epoxy type board is used as a mounting substrate.
The present invention has been made in view of the problems described above, and it is an object of the present invention to provide an ultrasonic vibration method and an ultrasonic vibration apparatus by which, where the apparatus is used as a bonding apparatus for a semiconductor chip wherein a plurality of bumps are arranged in an arbitrary arrangement, the bumps can be bonded while a sufficient bonding strength is assured without causing mechanical damage such as cratering to occur with all the pad electrodes to be electrically connected.
The present invention relates to an ultrasonic vibration method characterized in that a pair of ultrasonic horns are coupled in an intersecting relationship to each other, and a first one of the ultrasonic horns is excited to longitudinally vibrate in a lengthwise direction thereof to cause a second one of the ultrasonic horns to generate transverse vibrations while the second ultrasonic horn is excited to longitudinally vibrate in a lengthwise direction thereof to cause the first ultrasonic horn to generate transverse vibrations, such that composite vibrations of the transverse vibrations of the pair of ultrasonic horns that are produced at the intersecting coupling position of the pair of ultrasonic horns are used as an output.
Here, the pair of ultrasonic horns may intersect substantially perpendicularly with each other and produce the composite vibrations within a plane substantially in parallel to the plane which includes the pair of ultrasonic horns. A presser may be provided at the intersecting coupling position of the pair of ultrasonic horns and projected substantially perpendicularly to the plane, which includes the pair of ultrasonic horns; and, the presser may be pressed against a contact object member to transmit the composite vibrations to the contact object member. The contact object member may be bonded to another member by the composite vibrations.
A pair of ultrasonic vibrators for individually providing vibrations to the pair of ultrasonic horns may be provided, and the phase relationship between ultrasonic signals to be applied to the pair of ultrasonic vibrators may be adjusted. Adjustment of the phase of one of the pair of ultrasonic vibrators may be performed to adjust the phase relationship between the signals to the pair of ultrasonic vibrators. The amplitudes or the angular velocities of or the phase difference between the ultrasonic signals to be applied to the pair of ultrasonic vibrators may be adjusted to vary the locus of the composite vibrations in a plane parallel to the plane, which includes the pair of ultrasonic horns. The pair of ultrasonic horns may have a length substantially equal to the wavelength of ultrasonic waves which propagate in the pair of ultrasonic horns or substantially equal to an integral number of times the wavelength. Each of the pair of ultrasonic horns may be fixed at least at a position of a node. The pair of ultrasonic horns may intersect with and be coupled to each other, each at a substantially middle portion in the lengthwise direction thereof, such that the amplitude of the longitudinal vibrations is maximum at the intersecting coupling position, and each may be fixed by fixing means at a position spaced by a half wavelength or a distance of the sum of a half wavelength and an integral number of times one wavelength from the intersecting coupling position
The present invention according to a first principal aspect relating to an ultrasonic vibration apparatus relates to an ultrasonic vibration apparatus characterized in that it comprises a pair of ultrasonic horns coupled in an intersecting relationship to each other, and a first one of the ultrasonic horns is excited to longitudinally vibrate in a lengthwise direction thereof to cause a second one of the ultrasonic horns to generate transverse vibrations while the second ultrasonic horn is excited to longitudinally vibrate in a lengthwise direction thereof to cause the first ultrasonic horn to generate transverse vibrations, such that composite vibrations of the transverse vibrations of the pair of ultrasonic horns that are produced at the intersecting coupling position of the pair of ultrasonic horns are used as an output.
Here, the pair of ultrasonic horns may intersect substantially perpendicularly with each other and produce the composite vibrations within a plane substantially in parallel to the plane which includes the pair of ultrasonic horns. The ultrasonic vibration apparatus may further comprise a presser provided at the intersecting coupling position of the pair of ultrasonic horns and projected substantially perpendicularly to the plane, which includes the pair of ultrasonic horns; and, the presser may be pressed against a contact object member to transmit the composite vibrations to the contact object member. The contact object member may be bonded to another member by the composite vibrations.
The ultrasonic vibration apparatus may further comprise a pair of ultrasonic vibrators for individually providing vibrations to the pair of ultrasonic horns, and the phase relationship between ultrasonic signals to be applied to the pair of ultrasonic vibrators may be adjusted. Adjustment of the phase of at least one of the pair of ultrasonic vibrators may be performed. The amplitudes or the angular velocities of or the phase difference between the ultrasonic signals to be applied to the pair of ultrasonic vibrators may be adjusted to vary the locus of the composite vibrations in a substantially same plane.
The pair of ultrasonic horns may have a length substantially equal to the wavelength of ultrasonic waves which propagate in the pair of ultrasonic horns or substantially equal to an integral number of times the wavelength. Each of the pair of ultrasonic horns may be fixed at least at a position of a node by fixing means. The pair of ultrasonic horns may intersect with and be coupled to each other, each at a substantially middle portion in the lengthwise direction thereof such that the longitudinal vibrations exhibit a maximum amplitude at the intersecting coupling position, and each may be fixed by fixing means at a position spaced substantially by a half wavelength or a distance of the sum of a half wavelength and an integral number of times one wavelength from the intersecting coupling position. An odd-numbered order natural frequency of the transverse vibrations of the first ultrasonic horn may substantially coincide with the frequency of an ultrasonic vibrator of the second ultrasonic horn, which intersects with the first ultrasonic horn, such that the transverse vibrations thereof substantially resonate with the ultrasonic vibrations of the second ultrasonic horn.
The present invention according to another principal aspect relating to an ultrasonic vibration apparatus relates to an ultrasonic vibration apparatus characterized in that it comprises a pair of ultrasonic horns coupled in a substantially intersecting relationship to each other in a predetermined plane, an ultrasonic vibrator attached to an end portion of each of the ultrasonic horns, an ultrasonic oscillator for supplying ultrasonic signals to the pair of ultrasonic vibrators, and a presser provided at the intersecting coupling position of the pair of ultrasonic horns for being pressed against a contact object member, and that the pair of ultrasonic horns are excited to individually vibrate longitudinally such that the contact object member is bonded through the presser by composite vibrations of transverse vibrations produced at the intersecting coupling position.
Here, the ultrasonic vibration apparatus may further comprise phase adjustment means for adjusting the phase of the ultrasonic signals to be applied to the pair of ultrasonic vibrators. The phase adjustment means may be provided between at least one of the ultrasonic vibrators and the ultrasonic oscillator. The amplitudes or the angular velocities of or the phase difference between the ultrasonic signals to be applied to the pair of ultrasonic vibrators may be adjusted to vary the locus of the composite vibrations in the predetermined plane.
One of the ultrasonic horns may have a length substantially equal to the wavelength of ultrasonic waves which propagate in the ultrasonic horns or substantially equal to an integral number of times the wavelength. Each of the pair of ultrasonic horns may be fixed at least at a position of a node by fixing means. The pair of ultrasonic horns intersect with and may be coupled to each other each at a substantially middle portion in the lengthwise direction thereof such that the amplitude of the longitudinal vibrations is maximum at the intersecting coupling position, and each may be fixed by fixing means at a position spaced by a half wavelength or a distance of the sum of a half wavelength and an integral number of times one wavelength from the intersecting coupling position. An odd-numbered order natural frequency of the transverse vibrations of a first one of the ultrasonic horns may substantially coincide with the frequency of the ultrasonic vibrator of a second one of the ultrasonic horns which intersects with the first ultrasonic horn, such that the transverse vibrations thereof substantially resonate with the ultrasonic vibrations of the second ultrasonic horn.
A preferred form of the invention included in the present invention relates to an ultrasonic vibration method and an ultrasonic vibration apparatus for bonding a semiconductor chip which forms a flip chip IC to an electronic circuit board using ultrasonic waves, configured such that it comprises a pair of ultrasonic oscillators, a phase adjustment apparatus for adjusting the phase difference between ultrasonic signals outputted from the ultrasonic oscillators, two ultrasonic vibrators for generating ultrasonic waves in response to the ultrasonic signals from the ultrasonic oscillator, and a pair of ultrasonic horns intersecting in a substantially cross-shape with each other on an X-Y plane; and ultrasonic vibrations are attached individually to the ultrasonic horns and the amplitude and the angular velocity of the vibrations in the X-axis direction, the amplitude and the angular velocity of the vibrations in the Y-axis direction and the phase difference between the vibrations in the X-axis direction and the Y-axis direction are individually adjusted to appropriate values such that the semiconductor chip is pressed in vibrations against the electronic circuit board with an optimum locus in the X-Y plane to improve the bonding strength and the uniformity in bonding between the semiconductor chip and the electronic circuit board.
Here, the ultrasonic horns for the X-axis direction and the Y-axis direction that are coupled in an intersecting relationship in a substantially cross-shape to each other may have a length substantially equal to an integral number of times the wavelength of ultrasonic waves which propagate in the ultrasonic horns; and, besides each may be fixed at a position spaced by a xc2xd wavelength or a distance of the sum of a xc2xd wavelength and a distance of an integral number of times one wavelength from the center of the ultrasonic horns. Further, the pair of ultrasonic horns disposed in an intersecting relationship with each other generate such vibrations that longitudinal vibrations in one of the X-axis direction and the Y-axis direction by ultrasonic waves cause the ultrasonic horn for the other of the X-axis direction and the Y-axis direction to generate transverse vibrations, and composite vibrations produced by synthesis of the transverse vibrations of the ultrasonic horn for the X-axis direction and the transverse vibrations of the ultrasonic horn for the Y-axis direction form an arbitrary locus in the X-Y plane. Further, where an odd-numbered order natural frequency of the transverse frequency of the ultrasonic horn in this instance is set coincident with the frequency of the ultrasonic oscillator, the transverse vibrations resonate with the ultrasonic vibrations. Consequently, an ultrasonic vibration apparatus, which generates preferred vibrations is obtained.
Where such an ultrasonic vibration method and an ultrasonic vibration apparatus as described above are used for bonding of a semiconductor chip formed from a flip chip IC and an electronic circuit board, even if the arrangement of bumps of the semiconductor chip differs in various manners, since the direction of the ultrasonic vibrations includes components of the two directions of the X-axis direction and the Y-axis direction, a bonding quality having a stable bonding strength and a uniformity in bonding is achieved without being influenced by the direction of arrangement of the bumps.